Photocatalytic composition

ABSTRACT

Cleaning compositions including a photocatalytic material and a sensitiser employ a photocatalytic material and a sensitiser at a locus, for example on a surface. The residue combats soils and/or undesired microorganisms at the locus. The photocatalytic material is peroxo modified titania, preferably in its anatase form, or peroxo modified titanic acid, or a mixture thereof. The compositions are preferably alkaline.

The present invention relates to photocatalytic compositions and inparticular, but not exclusively, to photocatalytic cleaningcompositions, intended to reduce the frequency and/or effort ofcleaning; and to methods employing such compositions. References will bemade herein to cleaning compositions and/or to compositions which areeffective in combating malodours and/or soils and/or microorganisms,these being preferred compositions, but descriptions and definitionswhich follow are applicable also to compositions intended for otherpurposes.

Cleaning compositions of the invention are of particular interest forcleaning surfaces such as ceramic tiles, sinks, baths, washbasins,toilets, work surfaces, ovens, hobs, carpets, fabrics, floors, paintedwoodwork, metalwork, laminates, glass surfaces and the like.

Cleaning compositions intended for general and for specific uses arewell known in the art. Such compositions, when liquid, will commonlycomprise one or more surfactants, to loosen and/or disperse oilydeposits and to dissolve water soluble materials. These cleaningcompositions may include one or more of solvents (including water),thickening agents, abrasive particles, bleaching agents,disinfectants/antibacterial agents, perfumes, waxes or other polishingagents, preservatives, colouring agents and like additives. The liquidformulation provides a vehicle for the removal of insoluble particulatematter and builders and suspending agents are often included in thecompositions to facilitate this process. These prior art compositionsare, to a greater or lesser extent, effective in removing soils, usuallyorganic soils, from surfaces and in preventing their redeposition duringthe cleaning process. However, re-soiling of the surfaces after cleaningis an inevitable and continuous process.

Thus, domestic and other surfaces are continually dirtied or soiled byvarious means including, for example, soiling resulting from thepreparation of food, contact by people and domestic pets, deposition ofoily deposits and of airborne materials. Not only are these and likesoils aesthetically displeasing, they may also have deleterious effectson health. The soils may contain allergenic material such as pollen,dust mites, dust mite droppings, cat and other animal allergens andfurthermore may include harmful or toxic materials derived from adjacentor nearby industrial, horticultural or agricultural processes. Depositedsoils may also harbour and give sustenance to pathogenic microorganismsor might include residues of human or animal faeces or urine. It istherefore important that these and like deposited soils are removed fromsurfaces efficiently and frequently.

Cleaning of surfaces is therefore a frequent and often time consumingrequirement and is inevitably regarded as an unpleasant chore. There isa need for means to reduce the frequency of cleaning, and desirably alsoto facilitate the removal of soils deposited on surfaces. It will beappreciated that known, conventional, cleaning compositions have noeffect on soils deposited on the surfaces after the cleaning processuntil such time as the cleaning process is undertaken again. The presentinvention therefore seeks to provide cleaning compositions which, afterthe cleaning process, are effective to reduce the required frequency ofcleaning and/or to facilitate the removal of deposited soils.

It is an object of embodiments of the invention to provide a compositionshowing improved photocatalytic action.

In accordance with a first aspect of the present invention there isprovided a liquid composition which in use is applied to a surface anddries to leave a residue, wherein the composition comprises in admixture

-   -   (1) a photocatalytic material comprising up to 5% wt of the        composition; or a precursor to a photocatalytic material, the        photocatalytic material thereby produced comprising up to 5% wt        of the composition;    -   (2) a sensitiser which acts to absorb visible or ultra violet or        infra-red radiation and enhance the photocatalytic action of the        photocatalytic material, the sensitiser comprising up to 1% wt        of the composition.

It is an object of embodiments of the invention to provide a cleaningcomposition which, in addition to combating existing malodours and/orsoils and/or undesired microorganisms when applied to a locus, forexample a surface, combats further malodour compounds and/or soilsand/or undesired microorganisms, after its application to a locus.

In accordance with a second aspect of the present invention there isprovided a composition comprising a photocatalytic material able tocombat malodours and/or soils and/or undesired microorganisms at alocus, or a precursor to such a photocatalytic material, a sensitiserwhich acts to absorb visible or ultra-violet or infra-red radiation andimprove the efficacy of the photocatalytic material in combatingmalodours and/or soils and/or undesired microorganisms at the locus, andan alcohol; the photocatalytic material, sensitiser and alcohol being asdefined herein.

By “combat” we mean that the composition of the second aspect can beused to remove and/or break down malodour compounds and/or soils and/ormicroorganisms at the locus and/or it can prevent malodours and/or soilsand/or microorganisms from building up at the locus. The term“microorganism” is used in this specification to denote any microscopicorganism which is combatted; but especially a bacterium. Also ofinterest, however, as microorganisms which are prospectively combattedby compositions of the invention, are viruses and fungi, in particularyeasts. One pathogenic microorganism which is of particular interest asdemonstrating the efficacy of the compositions of the present inventionis the bacterium Staphylococcus aureus.

Said composition of the second aspect includes deodorising compositionsand anti-allergenic compositions. For example the compositions may havea deodorising effect, by breaking down odoriferous compounds, asdeposits and/or as airborne compounds. For such uses the compositionsmay be applied to surfaces in the appropriate location or may be used inroom sprays.

By means of the present invention a residue or layer of photocatalyticmaterial can be provided at a locus, for example on a surface wherebysoils and/or undesired microorganisms deposited on the residue or layeror soils or undesired microorganisms which are present on the surfaceprior to deposition of the residue or layer are subject to aphotocatalytic or other photochemical oxidation, reduction, free radicalor other photochemical reaction effective to break down, “burn away” orotherwise decompose the soils or undesired microorganisms or at leastmajor components thereof; and/or to weaken their contact with thesurface. Consequently it may be said that the cleaning process continuesafter the conventional act of removal of the soil or undesiredmicroorganisms is completed.

As noted above soils may contain allergenic material which is decomposedor otherwise degraded by means of the present invention. Of particularinterest is the use of the compositions of the invention in combatingallergenic soils associated with house dust mites.

It is believed that the faeces of two particular house dust mitespecies, Dermatophagoides farinae (known as Der-f) and Dermatophagoidespteronyssinus (known as Der-p) trigger the immune responses of the body,thereby giving rise to well known allergenic responses.

A review of this is given in Experimental and Applied Acarology, 10(1991) p. 167–186 in an article entitled “House dust-mite allergen”, areview by L. G. Arlian.

Both the Der-f and Der-p species are found throughout the world. In someareas, Der-f will be the sole Dermatophagoides species. In other areasDer-p will be the sole species. In still other areas, the two speciesare both present through, generally, one or the other will predominate.

Using the photocatalytic material, a decomposition reaction undergone bya malodour compound or a soil may involve photo-induced oxidation and/orphoto-induced reduction reactions with organic or inorganic componentsof the malodour compound or soil. These reactions may in turn result inthe production of free radicals which are effective in breaking downorganic matter in the malodour compound or soil. These reactions mayalso provide an ongoing benefit after the initial deodorising orcleaning process has been completed.

A possible mode of action using the photocatalytic material is nowdescribed. Whilst we are not bound by any scientific theory, in thissuggested mode of action, incident light of appropriate energy canpromote an electron from a valence band of the photocatalytic materialto a conductance band. There is then an electron (e⁻) in the conductanceband and a hole (h⁺) in the valence band. Both the electron and the holemay migrate to the surface of the photocatalytic material particle andinteract with oxygen and water to produce radical species. These radicalspecies may then generate free radical decomposition reactions in theorganic soil which may ultimately generate carbon dioxide if the freeradical reaction continues to its conclusion. It is believed that thesensitiser is able to absorb light from the visible or ultra violet orinfra-red (preferably the visible) region which causes an excitation ofthe sensitiser. Electrons are then emitted as the sensitiser decays ordecomposes from the excited state, and these electrons are transferredto the conductance band of the photocatalytic material.

In this invention the “photocatalytic material” is peroxo modifiedtitanium, preferably in its anatase form, or peroxo modified titanicacid, or a mixture therof, or a mixture of the above definedphotocatalytic material and titania, preferably in its anatase form, orzinc oxide, or a combination of the two, and is preferably present in atotal amount of from 0.01% to 20%, especially 0.2% to 3%, and mostpreferably 0.3 to 1%, by weight of the composition.

Photocatalytic material can be made by reference to the following

-   Journal of the Ceramic Society of Japan 104[8], 715–718 (1996)    Synthesis of Peroxo-Modified Anatase Sol from Peroxo Titanic Acid    Solution, by Hiromichi ICHINOSE, Makoto TERASAKI, Hiroaki KATSUKI.-   Journal of the Ceramic Society of Japan 104[10] 914–917 (1996)    Properties of Anatase Films for Photocatalyst from Peroxotitanic    Acid Solution and Peroxo-Modified Anatase Sol, by Hiromichi    ICHINOSE, Akihiko KAWAHARA, Hiroaki KATSUKI.

Preferably the photocatalytic material is imperceptible or almostimperceptible to the user after application. Preferably, thephotocatalytic material used in the present invention is of amicroscopic particle size. The microscopic particle size also assists inachieving a uniform dispersion throughout the formulation and inmaximising the efficiency of the photocatalytic reaction. Suitably thephotocatalytic material has a mean particle size (diameter) of at least5 nm, preferably at least 10 nm, most preferably at least 15 nm.Suitably the photocatalytic material has a mean particle size of lessthan 200 nm, preferably less than 100 nm. One especially preferred classof photocatalytic material particles has a mean particle size in therange 5–100 nm, in particular 30–100 nm.

The photocatalytic material may be positively charged (from acidic stocksolution) or negatively charged (from alkaline stock solution).

The photocatalytic material may be doped with an additional elementwhich has the effect of reducing the energy required to promote anelectron of the photocatalytic material to the conductance band, leavingthe corresponding hole in the valence band.

Preferably, the sensitiser is present in an amount up to 1%, morepreferably up to 0.1%, still more preferably up to 0.02%, and yet morepreferably up to 0.01%. Preferably it is present in an amount from0.00001%, more preferably from 0.0001%.

In this invention the sensitiser preferably absorbs radiation ofwavelength which is in the band 200–1200 nm, preferably 400–800 nm. Itsabsorbency peak within these bands may be narrow. Thus, it may typicallyabsorb within a sub-band 50–200 nm in width.

There are many sensitisers which will improve the efficacy of thephotocatalytic material. Examples may include cationic, anionic,nonionic and amphoteric dyes. Cationic dyes are one preferred class.Examples include the cationic dye/anionic borate dye complex sensitisersdescribed in U.S. Pat. No. 5,200,292. The cationic cyanine dyesdisclosed in U.S. Pat. No. 3,495,987 are also believed to be useful inthe present invention.

Other preferred sensitisers include the ruthenium sensitisers describedin J. Am. Chem. Soc., Vol. 122, No. 12, 2000, pp. 2840–2849. These havethree pairs of carboxylated bipyridyl groups complexed to a ruthenium(II) or ruthenium (III) atom. Two such complexes may be coupled togetherto make a polypyridine dyad, preferably an Ru(II)–Ru(III) polypyridinedyad.

Examples of preferred ruthenium sensitisers thus include the followingcompounds or salts thereof (conveniently halide salts, preferablychlorides):

-   ruthenium (III)    bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(1,2-bis[4-(4′-methyl-2,2′-bipyridyl)]ethane)-ruthenium(II)    bis-(4,7-dimethyl-1,10-phenanthroline)-   ruthenium (III)    bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(1,2-bis[4-(4′-methyl-2,2′-bipyridyl)]ethane)-ruthenium(II)    bis-(2,2′-bipyridine)-   ruthenium (II)    bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(4,4′-dimethyl-2,2′-bipyridine)-   ruthenium (II) bis-(2,2′-bipyridine)-(4,4′-dimethyl-2,2′-bipyridine)-   ruthenium (II) tris-(4,4′-dicarboxyl-2,2′-bipyridine)-   ruthenium (II) tris-(2,2′-bipyridine)-   ruthenium (II) bis-(4,4′-dicarboxyl-2,2′-bipyridine)-   ruthenium (II) bis-(2,2′-bipyridine)-   ruthenium (II) tris-(4,7-dimethyl-1,10-phenanthroline)-   ruthenium (II) bis-(4,7-dimethyl-1,10-phenanthroline).

Other classes of sensitisers of interest for use with a photocatalyticmaterial in the present invention the materials described in GB 1408144.They include eosin, rose bengal, fluorescein, chlorophyll, metal-freeporphyrin, sulphonated phthalocyanine and sulphonated zincphthalocyanine.

Other classes of sensitisers of interest for use with a photocatalyticmaterial in the present invention include organosilicon (IV)phthalocyanines and naphthocyanines having Q-band absorption maxima atwavelengths greater than 660 nm. Further information on thesesensitisers may be found in U.S. Pat. No. 5,916,481, the contents ofwhich are incorporated herein by reference.

Further information about useful sensitisers is found in WO 98/32829.The sensitisers described therein could be used in the presentinvention, and the descriptions thereof are preferably incorporatedherein by reference.

Preferably the composition includes a film-forming polymer. Suitablefilm-forming polymers include polyvinyl alcohol (PVA), polyvinylpyrrollidone (PVP), novolac resins, resole resins and polyvinyl phenolresins. A preferred film-forming polymer is PVP or chemically modifiedPVP.

When a film-forming polymer is employed it suitably comprises at least0.0005% wt of the composition, preferably at least 0.001% wt. It maytypically comprise up to 1% wt of the composition, preferably up to 0.2%wt of the composition.

In a third aspect of the present invention there is also provided acomposition which comprises in admixture

-   -   (1) a photocatalytic material comprising up to 5% wt of the        composition; or a precursor to a photocatalytic material, the        photocatalytic material thereby produced comprising up to 5% wt        of the composition;    -   (2) a sensitiser which acts to absorb visible or ultra violet or        infra-red radiation and enhance the photocatalytic action of the        photocatalytic material; and    -   (3) a humectant and/or hygroscopic compound.

Such compositions provide excellent deposition of the actives on thesurface without smearing. It is believed that the humectant acts toattract water to the deposited composition thus facilitating thecatalytic process.

Preferred humectants are monohydric and polyhydric alcohols as definedherein. Conversely, preferred monohydric and polyhydric alcohols for usein the first or second aspects herein are humectants and/or arehygroscopic.

Preferably the compositions additionally comprise an alcohol selectedfrom;

-   -   (i) a monohydric alcohol, comprising at least 30% of the        composition; or    -   (ii) a polyhydric alcohol, comprising up to 5% wt of the        composition.

In preferred embodiments the composition may contain a monohydricalcohol in addition to a said polyhydric alcohol. In such embodimentsthe monohydric alcohol is suitably present in an amount of at least 0.1%wt, preferably at least 1% wt, and most preferably at least 2.5% wt, ofthe composition. In such embodiments the monohydric alcohol ispreferably present in an amount up to 20% wt, more preferably up to 12%wt, and most preferably up to 8% wt, of the composition.

In embodiments in which at least 30% wt of a is monohydric alcohol ispresent the monohydric alcohol is preferably present in an amount up to65% wt, more preferably up to 60% wt, of the composition. In suchembodiments the monohydric alcohol preferably provides at least 35% wtof the composition. A polyhydric alcohol could be present in suchembodiments—preferably in the amounts defined herein—but preferably isnot present.

When any composition of the invention, whether it contains a polyhydricalcohol as the only alcohol or, as is preferred, also a monohydricalcohol, the polyhydric alcohol preferably comprises up to 3% wt of thecomposition, and more preferably up to 2% wt of the composition. Mostpreferably it comprises up to 1% wt of the composition. In suchembodiments the polyhydric alcohol suitably provides at least 0.001% wtof the composition, and preferably at least 0.01% wt of the composition.

Preferably a monohydric alcohol used in the invention has from 1 to 8carbon atoms, preferably from 1 to 6 carbon atoms. It may be linear orbranched. Especially preferred are ethanol and isopropanol.

When a polyhydric alcohol is present in a composition of the inventionit suitably has 2–4 hydroxyl groups, and 2–8 carbon atoms. Speciallypreferred are trihydric alcohols, preferably having 3–6 carbon atoms.Glycerol is especially preferred.

Although branched or, especially, linear alcohols are referred for usein the present invention cyclic alcohols are not excluded.

The compositions of the present invention are suitably provided in anyappropriate wet form. They may be dispensed in conventional mannerdirectly from a bottle or by means of, for example, a pump or a triggerspray or roller or an aerosol. Also, they could be applied to a surfaceby a brush, pad, impregnated woven or non-woven cloth, or sponge, papertowel, tissue paper or impregnated or non-impregnated wipe, pre-packed.

One or more components of the composition may be provided in one of theabove, for example by being impregnated in an absorbent body, and othercomponent or components may be provided in another of the above, forexample in a trigger spray bottle.

According to another aspect of the present invention there is provided akit for use in carrying out the method, the kit comprising at least twoelements which together provide components (1), (2) and (3) definedabove in the definition of the first or third aspect.

Liquid compositions are especially preferred, especially aqueous liquidcompositions. Aqueous liquid compositions can be emulsions, includingmicroemulsions, and/or may contain solvents which solubilise thosesensitisers which do not dissolve in a water phase. Liquid compositionscould be supplied ready-for-use or dilutable. Liquid compositions may beoptically clear or opaque.

Whilst the person skilled in the art will be able to prepare aqueous andnon-aqueous liquid formulations tailored to the above dispensing forms,the compositions of the present invention generally comprise not morethan 99.7%, preferably 75% to 0.95% water, and cationic, anionic,nonionic or amphoteric surfactants, or compatible combinations thereof,in an amount of 0.05% to 80%, typically 0.5% to 10%. Surfactants shouldbe selected having regard to the nature of the compositions inparticular the photocatalytic agent or the precursor therefor, to ensurein-pack stability. In general, anionic surfactants are not suitable forincorporation in acidic compositions, especially those containingtitania. In general cationic surfactants are not suitable forincorporation in alkaline compositions, especially those containingtitania. Nonionic surfactants are especially preferred in compositionsof the present invention.

Examples of nonionic surfactants which may be employed in thecomposition include those which are water soluble or water miscible andinclude but are not limited to one or more of the following: amineoxides, block copolymers, alkoxylated alkanolamides, alkoxylatedalcohols, alkoxylated alkyl phenols, and sorbitan esters, for examplesorbitan mono oleate. In each case the respective alkyl group ispreferably a fatty alkyl group, suitably having from 7 to 24 carbonatoms, preferably 8 to 16, and may be branched or, more preferably,linear. Alkoxylate chains may be propoxylate chains, mixedethoxylate/propoxylate chains or, most preferably, ethoxylate chains.Good examples include linear fatty alcohol ethoxylates (e.g. NEODOL,from Shell) and secondary fatty alcohol ethoxylates (e.g. TERGITOL, fromUnion Carbide). Other examples include alkoxylated octyl and nonylphenols (e.g. IGEPAL, from Rhône-Poulenc).

Examples of cationic surfactants which may be used in the presentinvention include quaternary ammonium compounds and salts thereof,including quaternary ammonium compounds which also have germicidalactivity and which may be characterized by the general structuralformula:

when at least one of R₁, R₂₁ R₃ and R₄ is a hydrophobic, aliphatic, arylaliphatic or aliphatic aryl group containing from 6 to 26 carbon atoms,and the entire cationic portion of the molecule has a molecular weightof at least 165. The hydrophobic groups may be long-chain alkyl,long-chain alkoxy aryl, long-chain alkyl aryl, halogen-substitutedlong-chain alkyl aryl, long-chain alkyl phenoxy alkyl or aryl alkyl. Theremaining groups on the nitrogen atoms, other than the hydrophobicradicals, are generally hydrocarbon groups usually containing a total ofno more than 12 carbon atoms. The radicals R₁, R₂, R₃ and R₄ may bestraight chain or may be branched, but are preferably straight chain,and may include one or more amide or ester linkages. The radical X maybe any salt-forming anionic radical.

Examples of quaternary ammonium salts within the above descriptioninclude the alkyl ammonium halides such as cetyl trimethyl ammoniumbromide, alkyl aryl ammonium halides such as octadecyl dimethyl benzylammonium bromide, and N-alkyl pyridinium halides such as N-cetylpyridinium bromide. Other suitable types of quaternary ammonium saltsinclude those in which the molecule contains either amide or esterlinkages, such as octyl phenoxy ethoxy ethyl dimethyl benzyl ammoniumchloride and N-laurylcocoaminoformylmethyl)-pyridinium chloride. Othereffective types of quaternary ammonium compounds which are useful asgermicides includes those in which the hydrophobic radical ischaracterized by a substituted aromatic nucleus as in the case oflauryloxyphenyltrimethyl ammonium chloride, cetylaminophenyltrimethylammonium methosulphate, dodecylphenyltrimethyl ammonium methosulphate,dodecylphenyltrimethyl ammonium chloride and chlorinateddodecylphenyltrimethyl ammonium chloride.

Preferred quaternary ammonium compounds which act as germicides andwhich are useful in the present invention include those which have thestructural formula:

wherein R₂ and R₃ are the same or different C₈–C₁₂alkyl, or R₂ isC₁₂–C₁₆alkyl, C₈–C₁₈alkylethoxy, C₈–C₁₈alkylphenolethoxy and R₂ isbenzyl, and X is a halide, for example chloride, bromide or iodide, ormethosulphate. The alkyl groups R₂ and R₃ may be straight chain orbranched, but are preferably substantially linear.

A mixture of two or more surface active agents may also be used. Otherknown surface active agents not particularised above may also be used insome compositions; especially when one of them is a nonionic surfactant.Surface active agents in general are described in McCutcheon'sDetergents and Emulsifiers, North American Edition, 1982; Kirk-Othmer,Encyclopaedia of Chemical Technology, 3rd Ed., Vol. 22, pp 346–387.

Fluorosurfactants (FSOs) are preferred surfactants, especiallyfluorinated ethoxylated non-ionic sufactants.

Another preferred surfactant is a quaternary ammonium cationicsurfactant, for example as sold under the trade mark REWOQUAT, availablefrom Goldschmidt A G, defined as “fatty alcohols (ethoxylated) 40–60%concentration and quaternary ammonium compounds, cocoalkyl-bis(hydroxyethyl) methyl, ethoxylated, chlorides (>20%)”.

Preferred surfactants have a surface tension not exceeding 50 dynes/cm,preferably not exceeding 40 dynes/cm, and most preferably not exceeding30 dynes/cm.

Grease cutting, adhesion promoting or other solvents may also beincluded generally in amounts of not more than 99%, typically not morethan 50%, preferably not more than 12%, and most preferably not morethan 8%, of the composition. Examples include glycols and glycol ethers.

Other ingredients of the compositions may include dispersing agents,suspending agents, colorants, fragrances, malodour combating agents(cyclodextrin, active fragrance components), surface active/coatingpolymers for sustained protection/coating of a surface, materials withmould and mildew or limescale removing properties (biocides, extreme pHmaterials), thickening reagents, polishes, sequestrants, fabricsoftening agents, optical brighteners, laundry anti-fade agents,enzymes, thickeners, preservatives, bleaches, bleach activators, waxes,stabilising agents, propellants and further material(s) to combatundesired microorganisms. In particular variations of liquidcompositions of the invention, some or all of the ingredients may be ofhigh volatility whereby a residue of photocatalytic material can be leftbehind on a surface in a controlled manner. The residue of thephotocatalytic material should be well dispersed on the surface suchthat it is invisible or almost invisible to the naked eye.

Suitable dispersing agents may include hydroxyethyl cellulose, polyvinylalcohol, polyvinyl acetate and ethylene oxide-propylene oxide blockcopolymers. Such agents may aid in-pack stability and promote goodsurface contact, on application.

Suitable adhesion promoters may include materials selected frompolyvinyl alcohols, polyacrylic acids, ethylene oxide-propylene oxideblock copolymers, hydroxyethyl celluloses, protein polymers andpolysaccharide polymers. Preferred adhesion promoters may includepolyvinyl alcohols, alginates, gum arabic, and pectin.

Liquid compositions of the invention, ready for use, may be of pH in therange 1 to 13, preferably 2 to 12, most preferably 3 to 11. Preferredcompositions have pH values of 7 or more, and are more preferablyalkaline. The pH is preferably 8 or more. Thus preferred liquidcompositions of the invention, ready for use, are of pH in the range 8to 13, preferably 8 to 12, most preferably 8 to 11.

The pH may not be the same as that of as-supplied liquid compositions,because the latter may be diluted.

In one embodiment the composition is a bleaching composition containinga peroxygen compound, for example hydrogen peroxide or a generatorthereof, or peracetic acid or persuccinic acid.

The components of the composition should be selected, and/or thecomposition formulated, such that the composition is stable for asufficient period, without components being degraded or renderedunstable by the photocatalytic material and the sensitiser. Preferablythe compositions are packaged for sale in containers which shield thecompositions from electromagnetic radiation of wavelength which wouldpromote its photocatalytic action. All such measures are within theordinary competence of persons skilled in the art.

Liquid compositions preferably have suitable rheology to suspendparticles and/or to inhibit run off from upright surfaces, onapplication. To this end liquid compositions may be thixotropic, andpreferably exhibit shear thinning with a suitable, preferably low, yieldpoint.

Preferred compositions of the invention are colloidal suspensions ofphotocatalytic material particles.

Preferred colloidal suspensions of the photocatalytic material particlesfor use in the present invention are prepared by steps of hydrolysis oftitanium tetrachloride in ammonium hydroxide, washing the precipitatethus formed, decreasing the pH to 3.3 by addition of a mineral acid,preferably nitric acid, washing until the conductivity drops below 500μS, and peptisation by addition of a mineral acid, preferably nitricacid, either at room temperature for 7 days or at 60–70° C. for 30–90minutes. The resultant colloidal suspension of the photocatalyticmaterial typically has a photocatalytic material concentration of about10 g/l and a mean particle size of about 20 nm. This method is known asthe Woodhead method, after the inventor and patentee thereof.

Alternative colloidal suspensions of photocatalytic material particlesfor use in the present invention may be prepared by the “isopropoxide”method. This method involves the steps of hydrolysis of titaniumisopropoxide, suitably in ammonium hydroxide, washing the precipitatethus formed, filtration, and peptisation by addition of a mineral acid,preferably nitric acid, either at room temperature for 7 days or at60–70° C. for 30–90 minutes. The resultant colloidal suspension ofphotocatalytic material typically has a photocatalytic materialconcentration of 25–30 g/l and a mean particle size of about 20 nm, whenthe peptisation is at ambient temperature. When the peptisation is atthe elevated temperature, the resultant colloidal suspension typicallyhas a photocatalytic material concentration in excess of 100 g/l and amean particle size of about 90–100 nm, but with a wide particle sizedistribution.

Further alternative colloidal suspensions of photocatalytic materialparticles for use in the present invention may be prepared by theKormann method. In this method titanium tetrachloride is hydrolysed at0° C. under a nitrogen blanket. Dialysis is carried out for 3–12 hoursto remove undesired by-products of the hydrolysis. The resultingphotocatalytic material suspension is dried using a rotary evaporator,aided by a water bath held at 30° C. The resulting solid is re-suspendedin deionised water. No peptisation step is required. The resultingcolloidal suspension of photocatalytic material typically has aphotocatalytic material concentration of about 1 g/l and a mean particlesize in the range 30–70 nm.

In accordance with a fourth aspect of the present invention there isprovided a method of cleaning or sanitising a surface, the methodcomprising the steps of contacting the surface with the componentsdefined above, preferably but not necessarily as one composition, but soas to deposit a residue of the photocatalytic material on the surface,and allowing the photocatalytic material to combat soils or undesiredmicroorganisms present on or subsequently deposited on the surface.

In the case of soils the combating may be by catalysing or effecting anoxidation, reduction or other decomposition of the soils.

The method is suitably carried out with the surface and the compositionat ambient temperature and without any subsequent-heat treatment.

The method is suitably carried out under visible light of intensity atleast 5,000 lux. Preferably the method is carried out under ambientlight conditions, for example daylight and/or under room lighting.

Acidic conditions may be favoured for methods of cleaning or sanitisingbathrooms and lavatories.

Alkaline conditions may be favoured for methods of cleaning orsanitising laundry and kitchen environments.

Neutral or near-neutral conditions may be favoured for methods oftreating delicate fabrics and surfaces (for example marble, and certainpainted surfaces).

The skilled person may consult readily available zeta potential plotsfor chosen photocatalytic materials in order to ascertain available andoptimal ranges of surfactants. Furthermore, the skilled person may usedispersing agents to allow co-formulation of materials which mayotherwise be incompatible.

The colloidal and interfacial nature of the photocatalytic material willdetermine the nature of the sensitisers, surfactants and other materialswhich can be employed to good effect, having regard to in-packstability, surface coverage and adhesion and photocatalytic activity. Inthe case of any doubt, of course, trial and error can be used. However,by way of guidance we can make the following general statements.

Preferred acidic photocatalytic material-containing compositions includea cationic and/or a nonionic surfactant; and preferably no anionicsurfactant. A nonionic surfactant is in all cases a preferredconstituent.

Preferred alkaline photocatalytic material-containing compositionsinclude an anionic and/or a nonionic surfactant; and preferably nocationic surfactant (in contrast, with certain mildly alkalinecompositions containing zinc oxide cationic surfactants may also beused). A nonionic surfactant is in all cases a preferred constituent.

Neutral or near-neutral compositions may contain a surfactant of anytype, and preferably include a nonionic surfactant.

The surfaces treated in the method may be hard surfaces, for examplesurfaces of wooden objects, tiles, sanitaryware, painted objects,panels, kitchen surfaces, worktops, walls, floors, ceilings, roofs,windows, mirrors, shower cubicles and shower curtains, and cars. Thehard surfaces may be the surfaces of outdoor garden structures, forexample greenhouses, outdoor furniture, patios and paths, walls orhouse/garden surfaces, or roofing.

The surfaces treated in the method may be fibrous surfaces, for exampleclothes, furnishing fabrics and carpets.

As mentioned above and as is evidenced from the foregoing descriptionand following examples our main interest is in providing a consumablesurface cleaning composition which has, to paraphrase, a keep-clean orself-clean action. However, other compositions having a photocatalyticmaterial or a precursor to the photocatalytic material and a sensitiserin admixture are included in the scope of the invention. Suchcompositions may, for example, be permanently secured to the surface ofa substrate, for example of ceramic, glass or plastics. Securement maybe by chemical bonding and/or a quasi-mechanical process, such assputtering; or may be incorporated in an article, for example ofceramic, glass or plastics, during its manufacture. For example, thecomposition could be compounded with a plastics material prior to itsmoulding or extrusion. Also covered are compositions to be added towater, to sanitise and/or decolourise it and/or to combat soils and/ormicroorganisms on surfaces in contact with the water or to combatmalodors.

The following examples are illustrative of compositions according to theinvention in the form of a liquid. They may all contain sensitisers,colorants, fragrances and preservatives, preferably at concentrationsnot more than 1% each, with the balance of the formulations beingphotocatalytic material and water.

All percentages in this specification are expressed in weight ofcomponent per total weight of composition unless otherwise stated.

The invention will now be further described by way of example, withreference to the following non-limiting embodiments.

Unless otherwise stated the examples now described employ:polyvinylpyrrollidone, [PVP] herein, as film former; and the ethoxylatednon-ionic fluorosurfactant ZONYL FS0 available from DuPont, [FSO]herein; the peroxo-modified titania product having the trade name HCT-3,from K. K. Haneron, 3-67 Wakabayashi, Yao shi, Osaka shi. The productcontains peroxotitanic acid, in solution, and peroxo modified anatase insuspension, [Ti-peroxo] herein; or, for comparison purposes, a colloidalsuspension of titania prepared by the Woodhead route described earlier,involving hydrolysis of titanium tetrachloride, acidification, washingand peptisation, [Ti-comp] herein. The concentration of titania in theresulting material, was about 10 g/l and mean particle size was about 20mm.

The materials were diluted to a concentration of the titanium compound(in total if there is more than one) of 1 g/l for the experiments.

The sensitiser was dissolved in deionised water with the help ofsonication, to make up a solution of concentration 3.5×10⁻⁵M.

The preferred ruthenium sensitiser, [Ru-terpy] herein, was ruthenium(II) tris-(2,2′-bipyridyl) dichloride, having the CAS No. 97333-4-6-5,and the structure:

C₃₀H₂₄N₆Ru Exact Mass: 570.11 Mol. Wt.: 569.62 C, 63.26; H, 4.25; N,14.75; Ru, 17.74

Also used as sensitisers were:

-   ruthenium (II) bis-(4,7-dimethyl-10-phenanthroline) dichloride,    [Ru-phen] herein, and-   ruthenium (II) bis-(2,2′-bipyridyl) dichloride [Ru-bipy] herein.

Compositions were prepared by blending the ingredients. In eachcomposition the [PVP] concentration was 0.025% wt and the [FSO]concentration was 0.05% wt. Deionised water was the only additionalcomponent, to the materials described above.

Application to Glass

A non-woven kitchen cloth was immersed in the respective composition andsqueezed until the weight of composition remaining was about twice theweight of the dry cloth. The cloth was then wiped across a verticalglass surface in a systematic manner, from top to bottom, then from oneside to the other. The window was left to dry overnight. Fifteenpanellists were then asked to assess the level of smearing obtained, onthe following scale:

-   0—no smearing-   1—slight smearing-   2—moderate smearing-   3—heavy smearing-   4—excessive smearing.    Reference smear marks, at values 0 and 4, were present in the    vicinity of the marks being assessed, to assist the panel members.    The average results are set out below.-   [Ti-peroxo]+[Ru-bipy] composition—0.39-   [Ti-peroxo]+[Ti-terpy] composition—0.22-   [Ti-peroxo]+[Ru-phen] composition—0.17-   [Ti-comp]+[Ru-bipy] composition—1.35-   [Ti-comp]+[Ru-terpy] composition—1.19-   [Ti-comp]+[Ru-phen] composition—1.89    Effectiveness Against Marks on Glass

Fingerprints were applied to glass by a volunteer, in the followingmanner. The volunteer rubbed his forefinger vigorously and repeatedlyagainst his forehead, and then applied the finger to the glass eighttimes, in different places, to remove excess sebum from the finger. Thevolunteer then applied the finger to the portion of the glass previouslycoated with one of the compositions identified above, using the methoddescribed previously. The procedure was then repeated to obtain afingerprint on a sample of the glass treated with a differentcomposition, and so on.

Additionally, artificial sebum, obtained from Scientific Surfaces S/DInc., of New York, USA, was applied to glass. 1 g of artificial sebumwas melted in a 50 ml beaker on a hotplate. When the artificial sebumhad fully melted the beaker was tilted and rotated, to coat the insidesurfaces of the beaker. The artificial sebum was allowed to cool andsolidify. A person wearing rubber gloves rubbed a finger over theinternal side of the beaker and applied that finger to the glass eighttimes, in different places, to remove excess artificial sebum from thefinger, and finally to a portion of the glass previously coated with oneof the compositions identified above. The procedure was then repeated toobtain a mark on a sample of the glass treated with a differentcomposition, and so on.

Assessment was again made by a panel using a 0–4 ranking, 4 being a verydirty mark applied to clean glass, unchanging with time, and 0 beingglass of perfectly clean appearance. Such reference end-points werepresent in the vicinity of the marks being assessed, to assist the panelmembers.

Assessment was made by the panellists initially, when no degradation ofthe dirty mark could have taken place.

The results are stated below.

-   [Ti-peroxo]+[Ru-terpy] composition—artificial sebum print. Assessed    level: 1.2-   [Ti-peroxo]+[Ru-terpy] composition—fingerprint. Assessed level: 1.0-   [Ti-peroxo] composition, no Ru sensitiser—artificial sebum print.    Assessed level: 3.8-   [Ti-peroxo] composition, no Ru sensitiser—fingerprint. Assessed    level: 3.1

1. A liquid composition which in use is applied to a surface and driesto leave a residue, wherein the composition comprises in admixture: (1)a photocatalyic material selected from peroxo modified titania, peroxomodified titanic acid, a mixture of peroxo modified titania, peroxomodified titanic acid, a mixture of titania with one or both of peroxomodified titania and peroxo modified titanic acid, a mixture of zincoxide with one or both of peroxo modified titania or peroxo modifiedtitanic acid, and a mixture of titania and zinc oxide with one or bothof peroxo modified titania and peroxo modified titanic acid; (2) asensitiser which acts to absorb visible or ultra violet or infra-redradiation and enhance the photocatalytic action of the saidphotocatalytic material, selected from: (a) cationic dyes, anionic dyes,nonionic dyes, amphoteric dyes, ruthenium compounds having three pairsof carboxylated bipyridyl groups complexed to a ruthenium (II) orruthenium (III) atom, eosin, rose bengal, fluorescein, chlorophyll,metal-free porphyrin, sulphonated phthalocyanine, sulphonated zincphthalocyanine, organosilicon (IV) phthalocyanines and naphthocyanineshaving Q-band absorption maxima at wavelengths greater than 660 nm, aswell as salt forms and mixtures thereof; (b) one or more of thefollowing compounds or salts thereof: ruthenium (III)bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(1,2-bis[4-(4′-methyl-2,2′-bipyridyl)]ethane)-ruthenium(II)bis-(4,7-dimethyl-1,10-phenanthroline; ruthenium (III)bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(1,2-bis[4-(4′-methyl-2,2′-bipyridyl)]ethane)-ruthenium(II)bis-(2,2′-bipyridine; ruthenium (II)bis-(4,4′-dicarboxyl-2,2′-bipyridine)-(4,4′-dimethyl-2,2′-bipyridine);ruthenium (II) bis-(2,2′-bipyridine)-(4,4′-dimethyl-2,2′-bipyridine);ruthenium (II) tris-(4,4′-dicarboxyl-2,2′-bipyridine); ruthenium (II)tris-(2,2′-bipyridine); ruthenium (II)bis-(4,4′-dicarboxyl-2,2′-bipyridine); ruthenium (II)bis-(2,2′-bipyridine); ruthenium(II)tris-(4,7-dimethyl-1,10-phenanthroline); ruthenium (II)bis-(4,7-dimethyl-1,10-phenanthroline); and, (4) a cationic, anionic,nonionic or amphoteric surfactant, or combination thereof.
 2. A liquidcomposition according to claim 1, further comprising (3) a humectant, ahygroscopic agent or both.
 3. A liquid composition according to claim 2,comprising an alcohol having 2–8 carbon atoms and 2–4 hydroxyl groups.4. A liquid composition according to claim 2, comprising a trihydriclinear alcohol having 3–6 carbon atoms.
 5. A liquid compositionaccording to claim 2, comprising glycerol.
 6. A liquid compositionaccording to claim 1, wherein the composition comprises a fluorinatedsurfactant.
 7. A liquid composition according to claim 1 which furthercomprises one or more film forming polymers.
 8. A liquid compositionaccording to claim 7 comprising one or more film forming polymersselected from: polyvinyl alcohol, polyvinyl pyrrollidone, novolacresins, resole resins, and, polyvinyl phenol resins.
 9. A liquidcomposition according to claim 8 wherein the one or more film formingpolymers are selected from: polyvinyl pyrrollidone or chemicallymodified polyvinyl pyrrollidone.
 10. A liquid composition according toclaim 1, wherein the composition is alkaline.
 11. A liquid compositionaccording to claim 1 which comprises: (1) an anatase form of peroxomodified titania.
 12. A liquid composition according to claim 1 whereinthe sensitiser absorbs radiation which is in the band of 200–1200 nm.13. A liquid composition according to claim 12 wherein the sensitiserabsorbs radiation which is in the band of 400–800 nm.
 14. A liquidcomposition according to claim 12 wherein the sensitiser absorbsradiation in a sub-band 50–200 nm in width within the band of 200–1200nm.
 15. A liquid composition for cleaning surfaces selected from ceramictiles, sinks, baths, washbasins, toilets, work surfaces, ovens, hobs,carpets, fabrics, floors, painted woodwork, metalwork, laminates, glasssurfaces according to claim
 1. 16. A method of cleaning or sanitising asurface, comprising the steps of: contacting the surface, with a liquidcomposition according to claim 1 to deposit a residue of the titanicmaterial on the surface, and allowing the titanic material to combatsoils or undesired microorganisms present on the surface or subsequentlydeposited on the surface.